I am sure the Canon focus's a bit faster and more so with the TC.. but it is should do for the extra ££££ and loss of versitility. I was a bit worried when I started playing with the Canon as I had a sinking feeling that maybe I would end up wishing I had gone for the Canon but after reviewing the results from the Canon I am even more satisfied with the Sigma.

I have a nice collection of L glass but for me, the Sigma is a great addition.

I am not looking to make any cash from my tele work, it is purely for enjoyment and for me using a zoom makes it a lot more fun.. I plan on taking in a lot of motorsport next year and the zoom for me will make it less hassle and will save me having missed photos from not being able to zoom out.

I had the Canon 300mm f4 before and really did not find it as much fun, ended up carrying 2 bodies and missing shots.

For me I would much rather have the Sigma but if you need every ounce of IQ and have time to change lenses/TC's oh.. and an extra £2000ish then the Canon is great.